Hydrocarbon Processing - May 2022 - 45

Digital Technology
* Tackle every furnace throughout
the refinery to ensure proper
control over combustion and
oxygen concentration (e.g., for a
furnace with 80% efficiency,
a 5% reduction in oxygen from
3.5% to 3.33% can result in roughly
a 0.3% increase in efficiency)
* Control emissions in closed
loop within the APC applications
(not simply monitoring emissions)
wherever it makes sense to do so
* Reduce the overall cost of fuels
entering the fuel gas network or
being directly fired, whenever
flexibility to use different
types of fuel exists, and improve
overall profitability
* Significantly reduce CO2
emissions, considering that
around 2.78 t of CO2
are
emitted for each ton of fuel gas.
The 200,000-bpd refinery in our example
can reduce fuel gas flaring and
blowdown by more than 50%, improving
overall combustion efficiency and
process unit performance, reducing CO2
emissions by 19,000 tpy and achieving
savings of $4.6 MM/yr.
Typical available control handles
include:
* Natural gas entry points
* LPG vaporizers
* Fuel oil/fuel gas balancing in
double firing boilers/furnaces
* Streams manipulated to support
fuel gas network pressure
(e.g., propane, LPG)
* Fuel gas exchange streams to/from
various headers and sections.
Pre-requirements are usually minimal,
and a calorific value analyzer may be required
only if accurate and sufficiently
robust inferentials cannot be built based
on available density analyzers and lab
analysis. Nonlinear inferencing capabilities
of proprietary softwareb
can be leveraged
to build such inferentials.
FIGS. 3 and 4 show fuel gas header
pressure and calorific value before and
after deploying the APC solution.
Hydrogen network optimization. Hydrogen
network optimization is another
significant opportunity to improve overall
process efficiency and support decarbonization
objectives.
Most refineries are either hydrogen or
desulphurization capacity limited (some
are both). In all cases, hydrogen must be
produced and used optimally. A refiner's
planning/scheduling department typically
provides guidance on hydrogen producers'/consumers'
load and what to do
in case of excess or the lack of hydrogen,
but coordination remains infrequent,
manual and sub-optimal.
Due to the high cost of natural gas, the
cost of producing hydrogen is expensive
(presently topping $3,000/t in some sites
for pure hydrogen, depending on how hydrogen
is produced). Moreover, producing
1 t of hydrogen in a steam reformer
results in approximately 10 t of CO2
FIG. 3. Fuel gas pressure before and after
deploying the APC solution.
FIG. 2. Fuel gas networks' nonlinearities.
, having
significant impact on site emissions.
It is imperative to avoid wasting hydrogen
to fuel gas-every kilogram
counts since a reduction of just 200 kg/hr
of hydrogen results in overall savings of
$2 MM/yr in energy and CO2
benefits.
Besides the economic loss, hydrogen
discharges to the fuel gas network disturb
overall operations given that the hydrogen
calorific value is 2 times-3 times that
of a typical fuel gas. There is certainly the
need to dynamically coordinate hydrogen
producing and consuming units, which
are often under different operators' responsibilities.
Some challenges and peculiarities
must be considered, including:
* The hydrogen network can be
very complex, with multiple
headers at different pressures
and purities, up to 4-6 suppliers
(reformers, steam reformers,
partial oxidation units, gasifiers,
etc.) and up to 10-15 consumers
FIG. 4. Fuel gas calorific value before and
after deploying the APC solution.
(hydrocrackers, hydrotreaters,
desulphurization units, tail gas
treaters, isomerization units, etc.)
and compressors, pressure swing
adsorption (PSA)/membranes,
or other purification units.
* Hydrogen headers usually have
different pressures and qualities
and are interconnected through
valves or compressors.
* Disturbances in one of the
suppliers or consumers can impact
the entire system with variations
Hydrocarbon Processing | MAY 2022 45
Hydrocarbon Processing - May 2022

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